High density polyethylene (HDPE) made using certain late transition metal containing catalysts has lower water vapor and/or oxygen transmission rates than similar HDPEs made using other polymerization catalysts, thereby making them superior in uses, such as packaging, where lower water vapor and/or oxygen permeation rates are advantageous.
High density polyethylene (HDPE) is an important commercial product, large quantities being produced worldwide. HDPE is typically recognized (and is defined for the purposes of the present invention) as a substantially linear, semi-crystalline, polymer of ethylene (preferably a homo-polymer but also on occasion containing very minor amounts of other well-known comonomers), possessing a density of 0.94 g/mL or higher.
An important use of HDPE is in packaging, which may be divided into two general typesxe2x80x94rigid packaging such as bottles and tanks, and flexible packaging such as bags and pouches. The former may be formed by such methods as blow or injection molding, and the latter are usually formed from films having one or more layers, at least one of which is HDPE.
HDPE is a favored packaging material for many products because of low cost, relatively easy formability and good toughness, and for some products having low permeation rates for certain materials either deleterious to these products, or to keep the package""s contents from diffusing from the package and being lost, such as water and/or oxygen. Among the types of products where these low permeation rates are important are foods, both dry and liquid materials, and lubricating oils. For example for dry foods low water vapor transmission rates are important to keep the foods crisp, while low oxygen transmission rates are important for any foods that may oxidize, forming off colors and/or tastes or smells in the food. The lower the transmission rates of the packaging, the better the food will taste and/or look, and/or the longer the food may be stored before being used, and/or the thickness of the packaging may be reduced without deleteriously affecting absolute rates of transmission, all of course important advantages. In some instances, such as bottles for toiletries such as perfume or cologne, it may be desirable to keep water in and/or oxygen out. Other combinations will be obvious to the artisan.
U.S. Pat. No. 5,955,555, WO99/12981, WO99/46302, WO99/46303, WO99/46304, WO99/46308, WO99/62963 (corresponding to U.S. patent application Ser. No. 09/317,104, filed May 21, 1999 now U.S. Pat. No. 6,252,022), WO00/15646, WO00/24788, WO00/32641, G. J. P. Brito-vesk, et al., J. Chem. Soc., Chem. Commun., p. 849-850 (1998), and B. L. Small, et al., Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) vol. 39, p. 213 (1998) (all incorporated by reference herein for all purposes as if fully set forth), all report the polymerization of ethylene using iron and cobalt complexes of certain tridentate ligands. No mention is made of the use of the resulting polymers for packaging where improved (lower) water vapor and/or oxygen permeation rates of HPDE are of interest.
Disclosed herein is a package comprising a high density polyethylene obtainable (and preferably obtained) by polymerizing ethylene in the presence of a polymerization catalyst component which comprises an iron or cobalt complex of a compound of the formula (I) 
wherein:
R1, R2, R3, R4 and R5 are each independently selected from the group consisting of hydrogen, a hydrocarbyl, an inert functional group and a substituted hydrocarbyl; and
R6 and R7 are each independently selected from the group consisting of aryl and substituted aryl.
This invention also concerns a process for making a package, comprising the steps of:
(a) polymerizing ethylene in the presence of a polymerization catalyst component to form high density polyethylene, the polymerization catalyst component comprising an iron or cobalt complex of a compound of the formula 
wherein:
R1, R2, R3, R4 and R5 are each independently selected from the group consisting of hydrogen, hydrocarbyl, an inert functional group or substituted hydrocarbyl; and
R6 and R7 are aryl or substituted aryl; and
(b) forming said polyethylene into said package.
Preferably the package referred to above is a rigid storage tank or is otherwise based upon a multilayer sheet or film containing at least one layer of, or in which at least one of the layers comprises, the HDPE defined above.
This invention further concerns a process for lowering the water vapor and/or oxygen transmission rates of a package manufactured at least in part with a first HDPE, comprising the step of replacing, during the manufacture of said package, at least a portion of the first HDPE with a second HDPE obtainable (and preferably obtained) by polymerizing ethylene in the presence of a polymerization catalyst component which comprises an iron or cobalt complex of a compound of the formula (I) 
wherein:
R1, R2, R3, R4 and R5 are each independently selected from the group consisting of hydrogen, a hydrocarbyl, an inert functional group and a substituted hydrocarbyl; and
R6 and R7 are each independently selected from the group consisting of aryl and substituted aryl.
This invention still further concerns a process for lowering the water vapor and/or oxygen transmission rates of a package manufactured from one or more layers of a first HDPE, comprising the step of replacing, during the manufacture of said package, at least a portion of at least one of the layers of the first HDPE with a layer of a second HDPE obtainable (and preferably obtained) by polymerizing ethylene in the presence of a polymerization catalyst component which comprises an iron or cobalt complex of a compound of the formula (I) 
wherein:
R1, R2, R3, R4 and R5 are each independently selected from the group consisting of hydrogen, a hydrocarbyl, an inert functional group and a substituted hydrocarbyl; and
R6 and R7 are each independently selected from the group consisting of aryl and substituted aryl.
Herein certain terms are used which are defined below.
A xe2x80x9chydrocarbyl groupxe2x80x9d is a univalent group containing only carbon and hydrogen. As examples of hydrocarbyls may be mentioned unsubstituted alkyls, cycloalkyls and aryls. If not otherwise stated, it is preferred that hydrocarbyl groups (and alkyl groups) herein contain 1 to about 30 carbon atoms.
By xe2x80x9csubstituted hydrocarbylxe2x80x9d herein is meant a hydrocarbyl group that contains one or more substituent groups which are inert under the process conditions to which the compound containing these groups is subjected (e.g., an inert functional group, see below). The substituent groups also do not substantially detrimentally interfere with the polymerization process or operation of the polymerization catalyst system. If not otherwise stated, it is preferred that substituted hydrocarbyl groups herein contain 1 to about 30 carbon atoms. Included in the meaning of xe2x80x9csubstitutedxe2x80x9d are rings containing one or more heteroatoms, such as nitrogen, oxygen and/or sulfur. In a substituted hydrocarbyl, all of the hydrogens may be substituted, as in trifluoromethyl.
By xe2x80x9c(inert) functional groupxe2x80x9d herein is meant a group, other than hydrocarbyl or substituted hydrocarbyl, which is inert under the process conditions to which the compound containing the group is subjected. The functional groups also do not substantially deleteriously interfere with any process described herein that the compound in which they are present may take part in. Examples of functional groups include halo (fluoro, chloro, bromo and iodo), and ether such as xe2x80x94OR50 wherein R50 is hydrocarbyl or substituted hydrocarbyl. In cases in which the functional group may be near a transition metal atom, the functional group alone should not coordinate to the metal atom more strongly than the groups in those compounds that are shown as coordinating to the metal atom, that is they should not displace the desired coordinating group.
By a xe2x80x9ccocatalystxe2x80x9d or a xe2x80x9ccatalyst activatorxe2x80x9d is meant one or more compounds that react with a transition metal compound to form an activated catalyst species. One such catalyst activator is an xe2x80x9calkyl aluminum compoundxe2x80x9d which, herein, is meant a compound in which at least one alkyl group is bound to an aluminum atom. Other groups such as, for example, alkoxide, hydride and halogen may also be bound to aluminum atoms in the compound.
By xe2x80x9carylxe2x80x9d is meant a monovalent aromatic group in which the free valence is to the carbon atom of an aromatic ring. An aryl may have one or more aromatic rings which may be fused, connected by single bonds or other groups.
By xe2x80x9csubstituted arylxe2x80x9d is meant a monovalent aromatic group substituted as set forth in the above definition of xe2x80x9csubstituted hydrocarbylxe2x80x9d. Similar to an aryl, a substituted aryl may have one or more aromatic rings which may be fused, connected by single bonds or other groups; however, when the substituted aryl has a heteroaromatic ring, the free valence in the substituted aryl group can be to a heteroatom (such as nitrogen) of the heteroaromatic ring instead of a carbon.
By xe2x80x9crelatively noncoordinatingxe2x80x9d (or xe2x80x9cweakly coordinatingxe2x80x9d) anions are meant those anions as are generally referred to in the art in this manner, and the coordinating ability of such anions is known and has been discussed in the literature, see for instance W. Beck., et al., Chem. Rev., vol. 88 p. 1405-1421 (1988), and S. H. Stares, Chem. Rev., vol. 93, p. 927-942 (1993), both of which are hereby included by reference. Among such anions are those formed from aluminum compounds such as those described in the immediately subsequent paragraph and Xxe2x88x92, including (R51)3AlXxe2x88x92, (R51)2AlClXxe2x88x92, R51AlCl2Xxe2x88x92, and R51AlOXxe2x88x92, wherein R51 is alkyl. Other useful noncoordinating anions include BAFxe2x88x92 {BAF=tetrakis[3,5-bis(trifluoromethyl)phenyl]borate}, SbF6xe2x88x92, PF6xe2x88x92, and BF4xe2x88x92, trifluoromethanesulfonate, p-toluenesulfonate, (RfSO2)2Nxe2x88x92, and (C6F6)4Bxe2x88x92.
By xe2x80x9cneutral Lewis basexe2x80x9d is meant a compound, which is not an ion, which can act as a Lewis base. Examples of such compounds include ethers, amines, sulfides, and organic nitriles.
By xe2x80x9ccationic Lewis acidxe2x80x9d is meant a cation that can act as a Lewis acid. Examples of such cations are sodium and silver cations.
By a xe2x80x9cpackagexe2x80x9d is meant any container that is meant to be sealed most of the time (sometimes called xe2x80x9cprotective packagingxe2x80x9d), especially before the contents are used, against ambient conditions such as air and/or moisture, and/or loss of the package""s content as by evaporation. The package may be designed so that the seal against ambient conditions may be broken permanently broken as by cutting or tearing to open a sealed bag, or may be broken temporarily, as by opening a screw-cap bottle and then replacing the cap. The package may have one or more inlets and/or outlets to store a material that may be added to and/or withdrawn from the package without further opening the package. The package may be formed in any manner (see below).
The polyethylene used herein is obtainable, and preferably obtained, by polymerizing ethylene in the presence of a catalyst component comprising an iron or cobalt complex of (I).
Such iron and cobalt complexes may be formed by a variety of methods, for example, the complex may be formed before the polymerization is performed, with the preformed complex being added to the polymerization process, or the complex may be formed in situ in the polymerization process, such as disclosed in previously incorporated U.S. Pat. No. 5,955,555 and WO99/12981, or in WO99/50273 (corresponding to U.S. patent application Ser. No. 09/277,910, filed Mar. 29, 1999) and WO00/08034 (also incorporated by reference herein for all purposes as if fully set forth), and reference may be had thereto for further details regarding these catalyst complexes and the preparation thereof.
In preferred embodiments, the catalyst complexes are referred to herein by the formula (I)MXn, wherein (I) is the compound (I), M is selected from the group consisting of Fe and Co, n is 2 or 3, and each X is independently an anion. Preferably each X is independently a halide, and more preferably chloride. This formula can be depicted by the structure (II) below: 
wherein R1, R2, R3, R4, R5, R6 and R7 are as defined above, and n is 2 or 3.
The following are preferred embodiments of (I):
R1, R2 and R3 are hydrogen; and/or
R4 and R5 are each independently selected from the group consisting of hydrogen and methyl, and both are more preferably methyl; and/or
R6 and R7 are each independently selected from aryl, and halo-substituted aryl, and more preferably aryl and halo-substituted phenyl, and especially aryl.
In (I) and (II), it is preferred that R6 is 
and R7 is 
wherein:
R9, R10, R11, R14, R15, R16, R19, R20, R21 and R22 are each independently hydrocarbyl, substituted hydrocarbyl or an inert functional group; provided that any two of R9, R10, R11, R14, R15, R16, R19, R20, R21 and R22 vicinal to one another taken together may form a ring.
In particularly preferred embodiments, R9, R11, R14 and R16 are hydrogen; R19, R20, R21 and R22 are independently methyl, ethyl, propyl, isopropyl, halo or trihalomethyl; and R10 and R15 are independently hydrogen, methyl, ethyl, propyl, isopropyl, halo or trihalomethyl.
The compound (I) is preferably formed by contacting a 2,6-diacetylpyridine with an amino-substituted aryl compound under conditions so as to form imine linkages, as disclosed in previously incorporated such as disclosed in previously incorporated U.S. Pat. No. 5,955,555, WO99/12981, WO99/50273 (corresponding to U.S. patent application Ser. No. 09/277,910, filed Mar. 29, 1999 now U.S. Pat. No. 6,232,259 and WO00/08034, and reference may be had thereto for further details.
The polymerization catalyst component may optionally comprise other components such as, for example, co-catalysts and catalyst activators.
For example, the catalyst component may contain a compound W, which is a neutral Lewis acid capable of abstracting an Xxe2x88x92 from the catalyst complex to form WXxe2x88x92, provided that the anion formed is a weakly coordinating anion, or a cationic Lewis or Bronsted acid whose counterion is a weakly coordinating anion; and provided that when none of X is alkyl, acyl or hydride, said second compound is capable of transferring hydride or alkyl to M.
Preferred compounds W include alkylaluminum compounds and/or other neutral Lewis bases. For example, the complex (I)MXn wherein M is Co or Fe, n is 2 or 3, and X is halide, may be contacted with an alkylaluminum compound such as methylaluminoxane to form a highly active polymerization catalyst. Iron complexes are preferred, Fe[II] and Fe[III] complexes are more preferred, and Fe[II] complexes are especially preferred. A particularly preferred complex is [2,6-diacetylpyridinebis{(2,4,6-trimethyl)phenylimine}]iron dichloride, especially in combination with methylaluminoxane.
Additional details may again be found in previously incorporated U.S. Pat. No. 5,955,555 and WO99/12981, or in WO99/50273 (corresponding to U.S. patent application Ser. No. 09/277,910, filed Mar. 29, 1998 now U.S. Pat. No. 6,232,259) and WO00/08034.
The polymerization to form the HDPE used in the present invention may be carried out in the gas phase, or in the liquid phase especially in slurry. In one preferred method the catalyst system, especially the iron or cobalt complex, is supported on a solid (heterogeneous) support, such as silica, alumina, another polymer, or a metal halide. The polymerization may also be carried out in batch, semi-batch, continuous, or continuous polymerizations in series. Continuous polymerizations are preferred.
Useful and preferred systems and conditions for carrying out the ethylene polymerization are described in, for example, previously incorporated U.S. Pat. No. 5,955,555, WO99/12981, WO99/46302, WO99/46303, WO99/46304, WO99/46308, WO99/62963 (corresponding to U.S. patent application Ser. No. 09/317,104, filed May 21, 1999 now U.S. Pat. No. 6,252,022), WO00/15646, WO00/24788, WO00/32641, and reference may be had thereto for further details.
The package may be formed by any conventional method for forming packages from thermoplastics. For rigid containers such as bottles, sealable cartons, storage tanks especially for water, chemicals, fuels and solvents, cosmetic jars, barrels, and drums, the container may be blow molded or rotomolded. In extrusion blow molding for example the body of the container such as a bottle may just be the HDPE described herein, or may contain two or more layers, at least one of which is the HDPE described herein. The cap of a screw-cap or snap-cap bottle be made of the HDPE, as by injection molding, or thermoforming, or may be made of another material, such as another thermoplastic, a thermoseting resin, metal, etc., as appropriate. Two halves (or other fractional parts) of the container may be thermoformed from a sheet of the HDPE or a multilayer sheet containing at least one layer of the HDPE, and the parts joined by welding or by an adhesive or both.
Another form of packaging is flexible bags or pouches, many of which are heat sealed or sealed with adhesive after being filled with whatever they are to contain. These may be made from films or tubes of the HDPE, or multilayer films or tubes that contain at least one layer of the HDPE. A tube for example may be heat sealed at one end, filled with liquid or solid, and then heat sealed or sealed with adhesive at the other end. A film may be folded once, heat sealed along the sides, filled, and then heat sealed at the other end, or adhesive may be used for some of all of the seals. Pouches may be formed by similar methods, except they tend to be more rigid, because of the thickness of the material from which they are made and/or their configuration. The flexible packages may also be sealed by interlocking seals that may be opened and resealed, sometimes called zip lip seals.
All of the above types of packages, and other types of packages, may be made by methods known in the art for making packaging from thermoplastics, see for example H. Mark, et al., Ed., Encyclopedia of Polymer Science and Engineering, Vol. 10, John Wiley and Sons, New York, 1987, p. 684-720, which is hereby included by reference.
As such, HDPE-containing packaging having improved (lower) water vapor and/or oxygen transmission rates can be prepared by replacing, during the manufacture of the package, at least a portion of the HDPE with a second HDPE obtainable (and preferably obtained) as set forth above.
Replacement can be accomplished by substituting this second HDPE at the time of manufacture of the package. The second HDPE can simply be used in place of conventional HDPE, or can be blended with conventional HDPE in order to replace a portion of the same. For multilayer packaging as described above, one or more of the layers can be prepared solely from the second HDPE, or a blend of the second HDPE with conventional HDPE, then substituted for a layer of conventional HDPE.
The blend can be a standard physical blend, melt blend, or even a reactor blend prepared by polymerizing ethylene in the presence of the catalyst complex referred to above, along with a second active HDPE catalyst (co-catalyst) such as a Ziegler-Natta and/or metallocene-type catalyst known in the art. See, for example, previously incorporated WO99/12981, WO99/46302, WO99/46303, WO99/46304, WO99/46308, WO00/15646, WO00/24788, WO00/32641, as well as WO98/38228 and WO99/50318 (corresponding to U.S. patent application Ser. No. 09/619,509, filed Jul. 19, 2000), which are also incorporated by reference herein for all purposes as if fully set forth.
In the Examples the following tests were used:
Oxygen transmission was measured using an Oxtran(copyright) 2/20 Model T, high transmission rate tester (Mocon, Inc., Minneapolis, Minn. 55428 U.S.A.) at 23xc2x0 C. and 0% relative humidity using 100% oxygen (not air). Sample films were run in duplicate. The theory of the test is outlined in ASTM D3985-81 xe2x80x9cStandard test Method for Oxygen Gas Transmission Rate through plastic film and sheeting using coulometric sensorxe2x80x9d. Results are reported per 25 xcexcm thickness (1 mil). Values were corrected to a barometric pressure of 101 kPa (760 mmHg). Samples were conditioned for 2 h prior to testing. Test area was 100 cm2. Examine time was 60 min. Nitrogen gas flow was 20.1 smLm.
Moisture Vapor Transmission was measured using a Permatran(copyright) W 3/31, water vapor transmission system (Mocon, Inc.) at 38xc2x0 C. and 90-100% RH. Sample films were run in duplicate. The theory of the test is outlined in ASTM D1249-90 xe2x80x9cStandard Test Method for Water Vapor Transmission through plastic film and sheeting using a modulated infrared sensorxe2x80x9d. Results are reported per 25 xcexcm (1 mil) thickness. Sample test area was 50 cm2. Relative Humidity was essentially 100%. Sample was conditioned 2 h before testing. Examine time was 30 min. Test temperature was 37.8xc2x0 C.
Unless otherwise noted polymer density was measured on samples prepared according to ASTM D1928, Procedure C, slightly modified. Polytetrafluoroethylene coated aluminum foil was used as the parting sheets, and the heatup time was 1.5 min at 180xc2x0 C., while eliminating the backup sheets and placing the sandwich of material and a 10 mil (250 xcexcm) chase of Teflon(copyright) FEP (available from E. I. DuPont de Nemours and Co., Wilmington, Del. 19898) between the two sheets of foil and placing it directly between the press platens. The density measurement was done following ASTM D1505. Density of extruded blown films was measured on the as made films using the method of ASTM D1505.
Melting point and heat of fusion of polymers was measured by differential scanning calorimetry, using values from the 2nd heat, and using a heating rate of 10xc2x0 C./min. The peak of the melting endotherm was taken as the melting point.
I2 and I10, which are melt indices at different shear stresses, were measured by ASTM method D1238.
In the Examples, all pressures are gauge pressures.
In the Examples Mn is number average molecular weight, Mw is weight average molecular weight, both determined by Gel Permeation Chromatography, PD is Mw/Mn, Tm is melting point, and xcex94Hf is heat of fusion.